The Defense Meteorological Satellite Program (DMSP) includes a block 5D-2 satellite having a special sensor microwave imager (SSM/I) which is used passively to measure microwave radiation in the 19-85 GHz range of the electromagnetic spectrum. The satellite then downlinks the digital data acquired for processing. Via the data processing of the output of the satellite, the radiation can be used to create colored images that contain accurately measured amounts of several meteorological parameters such as: surface wind speed, precipitation, water vapor, soil moisture, surface type, etc. These meteorological parameters are known as environmental data records (EDRs). The environmental data records are studied in conjunction with operational line scan (OLS) images generated from the satellite for applications such as weather forecasting.
In attempting to use both the SSM/I and OLS image types together, a number of difficulties arise. Specifically, each of the two image types are generally presented as distinct images. Current practice therefore requires a user to attempt to correlate the information visually by observing several separate images. Further, the user must filter out non-significant data and "invalid" data. For example, surface wind speed data is invalid over areas where there is significant rainfall. Therefore, it becomes very difficult for the user, e.g., a meteorologist or weather forecaster, to correlate the separate images for a specific geographical location scanned by the satellite.
Another difficulty in attempting to use both the SSM/I and OLS images together arises in that the resolution of the SSM/I and OLS sensors are significantly different. For example, the OLS smooth data has a resolution of 1.5 nautical miles and the SSM/I sensor has a resolution of 6.75 nautical miles from its sensor. Still further, the SSM/I sensor has seven distinct channels including four separate microwave frequencies that are used, for example 19, 22, 37 and 85 GHz. Three of the four microwave frequencies, i.e. 19, 37 and 85 GHz have both vertical and horizontal polarization and only one, i.e. 22 GHz, has just vertical polarization. Thus, the resolution of the channels within the SSM/I sensor also differ from the OLS sensor resolution.
Further, attempting to use the two image types together presents geolocation problems arising via the configuration of the sensors on the satellite. The OLS sensor is arranged on the satellite to point directly toward the center of the earth, i.e. it looks straight down on the curved surface of the earth. In contrast, the SSM/I sensor does not point toward the center of the earth, but rather is directed out of the end of the satellite at a 45.degree. angle to the vertical. Therefore, at any one point in time, the two images being recorded from the two sensors are for different locations on the earth's surface. For the OLS sensor, the curvature of the earth in the cross track direction, i.e., a line orthogonal to the satellite track (path), is significant and must be corrected. However, no earth curvature correction is required in the long track direction, i.e., the path the satellite follows over the earth at the subpoint (subpoint is the point on the earth's surface through which a line passes if drawn from the center of the satellite to the center of the earth), for the OLS sensor. For the SSM/I sensor, both long track and cross track corrections must be made to account for the curvature of the earth and SSM/I antenna orientation.
There is therefore needed a process and apparatus for solving the above-described problems and providing a single viewable image displaying both SSM/I and OLS images.